Thermally synthesized ruby microstructures and luminescence centers

Abstract

This work reports on the synthesis and the optical-structural investigation of light-emitting microstructures obtained from amorphous aluminum nitride (AlN) thin films doped with chromium. The samples were prepared by radio frequency sputtering an Al target, with approximately 0.8ppm of chromium, in an atmosphere of pure nitrogen. After deposition, the samples were thermally annealed up to 1050°C under a flow of dry oxygen. The experimental investigation included photoluminescence, cathodoluminescence, energy dispersive x-ray spectroscopy, and scanning and transmission electron microscopy techniques. According to the experimental data, films annealed at 1050°C for 15min exhibit relatively strong luminescence at ∼685nm. Further thermal annealing at this temperature induces the development of microscopic features onto the surface of the films that emit red light at approximately 693nm. In view of their distinctive luminescence characteristics and spatial dimensions, the observed features have been designated by ruby microstructures (RbMS’s). For the present AlN films, the occurrence of these RbMS’s is associated with Cr3+ ions in oxygen-rich environments (α-alumina) that arise in consequence of the thermal treatments and of the presence of microimperfections (pores, voids, etc.) in the samples.